This invention relates to bicycle frames. More particularly, this invention relates to a bicycle frame designed to provide improved handling and control characteristics.
In the past bicycle frames had been constructed of tubular members, either straight or curved, joined together to form a completed unit. Even racing bicycles, remain derivative of the classic diamond tubular frames.
Even special types of sports bicycles called BMX or free style bikes utilize variations on a diamond frame of triangulated tubular members.
Features desired in racing or sport bicycles are good handling, light weight, power train rigidity, and a low center of gravity. Features particularly desireable in BMX or sport-type free style bicycles is a standing platform or standing platforms, which are used for performing trick maneuvers. For these trick maneuvers it is desireable to have uncluttered standing room behind and below the seat and between the seat and the handle bars. Examples of such standing areas are shown in the GT Pro Series in red line BMX bikes illustrated on pages 6, 7, 8 and 9 of the March 1986 BMX Action Magazine.
Although there are conflicting theories and approaches to bicycle frame design, which remains as much an art as it is a science, one theory holds that frame stiffness directly corresponds to the efficiency of the power transmission from the rider's legs to the ground. Bicycles are subjected to reciprocating pedaling force, and standard bicycle designs with chain stays and seat stays, and in general, the diamond frame comprising tubular members welded or brazed together with or without lugs, is subject to a certain amount of distortion or deflection when subjected to the reciprocating periodic forces from the rider's legs pushing down on one side of the frame which is countered by the rider's grip upon the handle bars which pulls upward on the opposite side from the downward force. Although the deflection is somewhat spring like, there is an energy loss as not all of the energy is recaptured from the spring.
Stiffness is especially important in racing bicycle designs, and in off-road or trick bicycle designs. Racers, particularly when climbing or sprinting, lean the bicycle into the power leg up to 15.degree., increasing the need for lateral stiffness. Further, even minute energy losses add up, and in consideration of the length of some bicycle races, accumulative effects of such energy losses could be determinative of the outcome of the race.
Further evidence of the importance of fractional gains in efficiency can be seen in the radical frame and accessory designs seeking aerodynamic gains used in bicycles used for sprinting and professional races, such as the Tour de France. A change as simple as a different handle bar design was credited with providing the margin that allowed professional racer Greg LeMonde to win the 1989 Tour de France. See Sports Illustrated Vol. 71 No. 27, Dec. 25, 1989-Jan. 1, 1990. The Tour de France is an example of a long professional race where great sums of money are at stake, and fractional gains can add up to the difference between winning and losing over more than three (3) weeks of stage races, during which the riders cover an excess of 2,000 miles over widely varying terrain.
World class amateur and professional sprinters and bicycle racers are tremendously fit and can exert forces upon racing frames far greater than those of a recreational rider. The same is true for BMX and off-road bicycle riders whose bicycle frames are subjected to severe impact loads from jumps and bumps, both during recreational and racing.
The bicycle frame of the present invention can be configured to any wheel base, wheel diameter, head tube angle, seat tube angle, wheel width, rider weight, or specific use by varying the frame dimensions and/or materials as will be further described below. The frame design of the present invention utilizes a channel frame main member in combination with the seat tube, head tube and down tube used by diamond configured tubular frame designs. In comparison to the diamond configured tubular frame designs the present invention is lighter in weight which translates to lower energy demands, easier climbing, increased traction and road holding, and better handling in general. In addition, the channel member of the present frame design can easily be provided with means for mounting numerous accessories mandated by particular bicycle uses, or popular with racers and recreational riders. The flat sides of the channel frame provide easy mounting for derailleurs, and provide a protective enclosure for the power transmission components of a bicycle by covering the top of the chain sprocket at the crank, and by almost completely enclosing the rear hub or derailleur components. Optionally, standard derailleur components could be mounted to the outside face of one of the channel legs by a simple bolt on connection.
The channel frame components could also be injection molded or thermal molded from plastic materials for use in much smaller scale bicycles or tricycles for children and beginners. The protective covering over the drive chain, and the qualities of light weight, low center of gravity and good handling are equally important for beginners.